A large number of head straps, with which protective helmets, hoods or masks can be fastened to the head of the user of the respirator, have become known among respirator products. A head strap, which comprises individual strap elements, which can be adapted to the shape of the head of the user of the head strap, has become known from U.S. Pat. No. 4,279,037. Such head straps can be used by a large number of persons who need head protection. On the one hand, the head strap shall be able to be fastened nondisplaceably on the head of the user of the head strap, but, on the other hand, it shall be able to be easily removed. In persons who perform physical exercise and wear a head strap, there is increasingly a need for detecting and monitoring physical data in order to recognize physical overexertion in time. The body temperature is a physiological parameter from which the general condition can be deduced. Even though it has been known from medical treatment devices for infants that the skin temperature can be detected in the area of the abdomen by means of a temperature sensor placed there, these measurements are carried out only on subjects who are not moving or are moving only slightly. The temperature sensor is therefore fastened to the skin at this location with an adhesive strip only.